Mining tool

ABSTRACT

The invention concerns a mining tool having a body and having distributed about the body and projecting from the front side thereof a plurality of pick type bits, each rotatable in a respective bore. The tool preferably has a central pilot cutter disposed at least slightly in advance of the pick type bits. The tool may be made to various sizes by mounting rings on the body with the rings having pick type bits rotatably mounted thereon.

United States Paten n91 McKenry et a1. 1

[ ]March 13, 1973 1 MINING TOOL [75] Inventors: Robert J. McKenry, Windber;

Seibert S. Oaks, Everett, both of Pa.

[52] U.S. Cl. ..l75/335, 175/354, 175/415 51 Int. Cl. ..E2lb 9 12 [58] Field of Search ..l75/334, 335, 354, 376; 299/86, 92

[5 6] References Cited UNITED STATES PATENTS 1,747,908 2/1930 Seifert ..l75/334 1,790,613 l/l93l Gilderslecvc ct n1. ......l75/3 .14 X 3,139,148 6/1964 Robbins 175L170 X 3,342,531 9/1967 Krckelcrw ..Z99/)2 3,342,532 9/1967 Krekeler .299/92 Primary Examiner-Ernest R. Purser Att0rneyMelvin A. Crosby [57] ABSTRACT The invention concerns a mining tool having a body and having distributed about the body and projecting from the front side thereof a plurality of pick type bits, each rotatable in a respective bore. The tool preferably has a central pilot cutter disposed at least slightly in advance of the pick type bits. The tool may be made to various sizes by mounting rings on the body with the rings having pick type bits rotatably mounted thereon.

22 Claims 14 Drawing Figures 24 Q 20 III 20 0 J 22 I/ Q D y; 1 30 IO PATENTFUHARUISH 3,720,273

SHEET 1am I FIG-2 FIG-4 INVENTOR. ROBERT J.Mc.KENRY BY EBERT 5. OAKS PATEHTEUHAR 1 3191s SHEET 2 BF 6 FIG-3 FIG-5 SHEET 3 BF 6 INVENTOR. R BERT J. MQKENRY BY SIEBERT scams PATENTEUHAR 1 3 1975 SHEET 0F 6 FlG-8 INVENTOR. ROBERT JJMQKENRY BY EIEBERT 5. OAKS FATENTEUHARIBIHYS 3,720,273 'SHEET 5 [1F c INVENTORS ROBERT J. MCKENRY Y SEIBERT. S. OAKS WWW;

PATENTEnmmmu 3,720,273

' sumsnre INVENTORS ROBERT J. MCKENRY SEIBERT 5. OAKS Mi -M MINING TOOL RELATED APPLICATION This application is a continuation-in-part of copending application Ser. No. 796,032, filed Feb. 3, I969 and now abandoned.

This invention relates to a cutting, drilling, or boring device, and is particularly concerned with a tool for boring holes into earth, rock, and ore formations.

Mining and like operations are often accompanied by boring and drilling of holes into formations being worked. Where such formations are extremely hard, such as hard rock, the boring and drilling is usually carried out by using a percussion bit of some sort which is impacted against the formation thereby the break and crush the material of the formation.

In other cases, the material of the formation is somewhat softer and can be reduced somewhat more easily. Such softer formations might include, for example, potash or coal deposits or the like. The boring of the softer formations does not require percussion tools and has heretofore been carried out by means of auger type tools which might have carbide tipped leading edges. Such boring tools operate satisfactorily but have relatively short life due to abrasion of the tools by the material being cut.

The present invention is concernedprimarily with a novel boring tool for boring holes in either hard or soft formations such as those of the nature referred to.

A particular objective of this invention, therefore, is the provision of an improved boring tool or drill of the nature referred to above. 7

Another objective is the provision of a boring tool which remains sharp throughout its life.

Still another objective is the provision of a boring tool of the nature referred to which is inexpensive to construct and which includes readily replaceable cutters so that the cutters can be periodically renewed and thereby retain the boring tool in service. 7

Still another objective of this invention is the provision of a boring tool of the nature referred to which can be manufactured to a relatively small size for boring small holes and which can also be constructed to a much larger size for boring holes of substantial diameter.

A still further object of the invention is the provision of a renewable boring tool which can be made for use with an impact type tool as well as with a rotary tool.

The foregoing objects, as well as still other objects and advantages of the present invention, will become more apparent on reference to the following detailed specification taken in connection with the accompanying drawings in which:

FIG. I is an end view of a rotary boring tool according to the present invention looking in at the tool from the working side thereof;

FIG. 2 is a side view of the tool, partly broken away, and looking in at the tool from the right side of FIG. 1;

FIG. 3 is a view similar to FIG. 2, and is also partly broken away, and shows a boring tool constructed somewhat differently than that of FIGS. 1 and 2;

FIG. 4 is a sectional view indicated by line IV-IV on FIG. 1 showing a typical construction for one of the replaceable cutters of the boring tool and the support block therefor;

FIG. 5 is an end view of a boring tool according to the present invention made for large diameter holes;

FIG. 6 is a perspective view showing a tool according to FIGS. 1 or 3 mounted on the lower end of a drill string;

FIG. 7 is a perspective view showing an earth auger having a drilling tool according to the present invention built on the working end thereof;

FIG. 8 has a view similar to FIG. 5 but showing a dif ferent type of large diameter boring tool adapted for heavier work than the tool shown in FIG. 5;

FIG. 9 is a side elevational view showing a bit arrangement according to the present invention adapted for being impacted in use;

FIG. 10 is a view looking up from the bottom of FIG.

FIG. 11 is a transverse sectional view indicated by line XI -XI on FIG. 10 showing the portion of the bit in which the cutting tools are mounted;

FIG. 12 is a section indicated by line XII-XII on FIG. 11 showing how the holes in which the cutting tools are mounted are inclined to the vertical;

FIG. 13 is a sectional view indicated by line XIII- XIII on FIG. 2 showing the provision of air holes in the body of the bit; and

FIG. 14 is a side view showing one of the individual tool elements employed with the bit of the present invention.

The present invention, in brief, comprises a body having a central axis and having a working face at one end substantially perpendicular to the axis of rotation of the body. The tool of the present invention is particularly characterized in the provision of cutters detachably mounted on the body and projecting from the working face thereof so as to be engageable with the formation being bored.

In particular, thecutters according to the present invention have a cylindrical shank portion receivable in a cylindrical hole in the tool body and with each cutter having a projecting portion symmetrical about the axis of the cylindrical shank and tapering inwardly to a hard point at the outer end. Each cutter is rotatable in its respective hole and the hard cutting point is thereby maintained sharp at all times.

The cutters project from the front of the body of the tool and are inclined to the axis of the body and are thus presented point end foremost to the formation being worked and so as to dislodge material therefrom.

Advantageously, a pilot cutter head in the center of the body has stationary cutting blades and serves to pilot the body in the hole being bored.

Referring to the drawings somewhat in more detail, the tool shown in FIGS. 1 and 2, and which is a rotary tool, comprises a body 10, a steel. forging, for example, generally disc shaped and having welded to one side thereof a square shank 12 to permit the tool thereby connected to a driving device.

The side of the body 10 opposite shank 12 is the working face of the tool and in the center thereof there is welded the internally threaded sleeve 14 forming a chuck for receiving the threaded shank 16 of a pilot having a body 18 with a plurality of cutting elements 20 distributed circumferentially thereof. The cutting elements extend axially and radially of body 18 of the pilot.

Mounted on the working side of body and circumferentially spaced thereabout are support blocks 22. Five of the support blocks are shown in FIG. 1 but there could be more or fewer thereof, depending on the size of the body and individual preference. As will be noted in FIG. 2, the body 10, on the working side, tapers toward the center so that the blocks 22 are mounted on somewhat inclined surfaces and, therefore, incline outwardly from the center axis of body 10.

Each support block 22 has rotatably mounted therein a cutter or bit 24 which is a known type of pick type mining tool. Reference to FIG. 4, will show that each cutter or bit 24 has a cylindrical shank 26 disposed in cylindrical bore 28 in the respective support block 22. The portion of cutter 24 outside the block tapers generally inwardly toward the other end and in which other end there is mounted a pointed cutting tip 30 of a hard wear resistanct material such as cemented tungsten carbide, for example.

Bore 28 has a tapering mouth region 32 forming a seat and the cutter has a tapering portion 34 engaging the seat. The cutter is held in place in the block, while being free to rotate therein, as by a resilient keeper member 36 captive on shank 26 and having protuberances 38 adapted for engaging groove 40 in bore 28 when the cutter is inserted in the bore. The resilient keeper 36 is compressible on the bit shank to permit the cutter to be pushed into the bore into operative position therein, while a groove 42 on the cutter at the front of the block is adapted for receiving a prying tool to permit the cutter to be pried from its support block when it is to be replaced.

As will be seen in FIG. 1, the cutters indicated at A, B, and C have their hard cutting tips located on a circle D which represents about the size of the hole which will be bored by the tool. Circle D, it will be noted, is larger in diameter than any part of the tool escept the hard tips on the ends of cutters A, B, and C. The cutter E in FIG. 1 is arranged so that its point moves along a smaller circle than circle D, while cutter F is arranged so that its point moves in a still smaller circle.

The several support blocks 22 are so fixed to body 10 that the cutters incline on the body in the direction of rotation of the tool, the direction of the rotation being indicated by arrow R in FIG. 1.

The support blocks also hold the cutters so that they incline at different angles relative to the axis of body 10 and in this manner it is possible for cutters A, B, and C to sweep a large circle while cutters E and F sweep respectively smaller circles. The combination of the cutters and pilot provides for efficient boring of a formation so that boring can be accomplished extremely rapidly. I

Furthermore, due to the inclination of the cutters, and the rotatable support provided therefor by the blocks 22, the cutters rotate during operation of the boring tool and remain sharp and pointed throughout their life. The life of the cutters can be considered to be the length of time that any part of the hard cutting element remains therein at the tip end. When this hard material is used up from the cutter or if the cutter breaks, or becomes defective for any reason, it is merely pried out of its support block and another cutter is put in its place. I

The tool of FIG. 3 is the same as that of FIGS. 1 and 2, with respect to the arrangement and support of the pilot and cutters, and which bear the same reference numerals as they do in FIGS. 1 and 2. In FIG. 3, however, the body 10 is provided on the back with a tapering shank portion 50 having threads 52 for connection thereof to a tubular driving member. Further, fluid passage 54 is provided extending through the shank and the body and terminating in ports 56 so that fluid under pressure can be supplied to the working face of the bit to convey the material taken by the tool away from the working region.

Turning now to FIG. 5, while the tools of FIGS. 1, 2,

and 3 are relatively small, the tool of FIG. 5 is arranged for boring large holes. In FIG. 5, a tool is provided which, in the center, as generally indicated at 60, is provided with a drilling tool substantially the same as described previously. In FIG. 5, however, there is also provided an outer support ring 62 concentric with central tool 60 and supported thereon by two or more spoke members 64 extending radially between center tool 60 and ring 62.

Arranged in circumferentially distributed relation on ring 62 are support blocks 66, each of which rotatably supports a cutter 68. Each cutter 68 is inclined in the direction of rotation of the tool so as to dig into a formation to which the tool is presented. Furthermore, the cutters 68 are arranged at various inclinations to the axis of the tool so as to sweep a relatively wide radial range.

For example, the tool as illustrated has four cutters having their cutting tips sweeping along the circle 70 and has four other cutters having cutting tips which sweep along the circle 72, while four more cutters are provided whose cutting tips sweep along the circle 74.

Mounted on the spokes 64 are further support blocks 76 each carrying a cutter 78 and these cutters sweep the region between the aforementioned circle 74 and the outermost circle swept by the cutters of the central tool 60.

The arrangement of cutters in FIG. 5 insures that all of the material of the formation within the range of the tool will be broken out so that a clean hole will be taken by the tool.

It is evident that the basic cutting tool of the present invention, consisting of a body with support blocks and cutters mounted thereon and having a central pilot could be made relatively small, down to, say about 4 inches in diameter while, by the addition of one or more support rings as shown at 62 in FIG. 5, the tool could be made as large as desired. The tool shown in FIG. 5 is about 15 inches in overall diameter but the tool could be made even larger if so desired.

FIG. 6 shows a rotary tool 80 according to the present invention mounted on the end of a drill string 82. This figure shows the conical envelope within which the pilot cutter and bits are located with the pilot at the apex and with the outermost row of bits at the base. The novel arrangement of the tool according to the present invention wherein the cutting elements define a conical envelope is important because the pilot cutter leaves the remainder of the tool and forms a central hole in the formation being worked. Because of this central hole, the next bit or bits will break the formation radially inwardly toward the pilot hole and this can be done, of course, much more easily than a solid formation can be cut.

In FIG. 1, for example, which is an end view of a cutter of the type shown in FIG. 6, the bit marked F is the closest to the pilot cutter and its cutting and breaking action, as mentioned, will be toward the pilot hole. The next bit encountered when moving in the. radially outward direction is the one marked E and this bit will also cut and break material inwardly toward the space created by bit F.

Finally, the outermost cutter bits at A, B, and C will cut and break material inwardly toward the space created by bit E and this forms the maximum diameter of the hole being cut. This important principle of having the bits located so that they define a conical envelope with its apex toward the front of the tool and formed by the pilot cutter as a common characteristic of all of the tools illustrated. It has been found, by tests and experimentation, that greatly superior and more rapid cutting action is had by rotary boring or drilling tools constructed according to the present invention than with any other type known to us.

In particular, since the pilot cutter is in advance of all of the bits of the rotary tool, any failure of the tool occurs at the pilot cutter. Thisis in distinct contrast to the failure of rotary drills and boring tools according to the prior art wherein first failure occurs at the outer periphery of the tool. With the pilot cutter readily replaceable, it will be evident that a drilling and boring tool according to the present invention can have extremely long life and can be maintained relatively inexpensively.

In FIG. 7 an auger 84 is shown and the leading end thereof is provided with an arrangement according to the present invention. The front end of the auger is reinforced as by the plate and block means 86 and which include a central block having forwardly projectingposition 88 in which a rotary cutter 90 of the type shown in FIGS. 1 or 3 is mounted. On the edge of the blades of the auger at the forwardmost end, a plurality of bits are provided as indicated at 92.

These last mentioned bits define the maximum diameter which is cut by the auger and it will be noted that they incline outwardly from the auger axis and forwardly in the direction of rotation of the auger so that they are presented pointed ends foremost to the work.

. The tips of bits 92 are positioned substantially rearwardly from the central tool 90 and disposed therebetween and arranged on inclined paths are two rows of bits 94. Bits 94 sweep the region between the central rotary tool 90, and the outermost row of bits at 92.

The bits 94, as mentioned, are arranged in paths which incline backwardly of the auger so that the aforementioned conical envelope is again created which means that each bit outwardly from the pilot cutter 96 of tool 90 cuts and breaks material inwardly toward the 3. A relatively heavy plate structure 102 is provided and mounted about the periphery thereof are bits 104. Theplate has twov substantially quadrant shaped diametrically opposed regions, each of which carries two rows of bits 106. These bitsare arrangedon a plurality of holes bored therein, could be provided for i supporting the bits with the bars, in turn, being fixed to the body of the tool.

In FIGS. 9 through 14, the tool illustrated is similar to that first described, but is adapted for being impacted, like a down-the-hole bit, while rotating or being indexed slowly with the principal reduction of the formation being worked taking place due to crushing and breaking of the formation, rather than by digging of the formation as has been developed in connection with the first described modifications.

In FIG. 9, 10' indicates a drilling motor adapted for moving downwardly in a hole in the earth or rock which is being drilled. At the lower end of motor 10' is a shank 12' which is impacted in the vertical direction by operation of the drilling motor. Advantageously, either shank 12, or motor 10' together with shank l2, rotate as the shank is impacted so that entire area of the bottom of the hole being drilled will be engaged by the tool arrangement mounted on the lower end of shank 12'.

With reference to the tool arrangement, which differs from the first described modifications in that the bits, or cutters, are considerably less inclined in the circumferential direction so the tool can be impacted without breaking of the bits, or cutters, this takes the form of a base plate or body member 14 secured to the lower end of. shank 12 as by welding 16'. Other means of connecting base plate '14 to shank 12' can be availed of, but welding is a preferred manner of interconnecting these two elements.

Base plate 14', as will be seen in FIGS. 9 and 10, has a plurality of pick type tools or bits or cutters 18' mounted therein and distributed thereon circumferentially and radially. The pick type tools extend generally downwardly from base plate 14 and are inclined outwardly therefrom and, as will be I seen hereinafter, are also inclined slightly in the circumferential direction.

The tools 18' are arranged :in a first outer row marked A, a second next inner row marked B and an innermost row marked C. The relationship between rows A, B and C will be best seen in FIG. 9, wherein a pick of each of rows B and C with relation to a tool of row A.

In the center of base plate 14 and extending axially therefrom is a pilot cutter 20' which projectsaxially beyond the lowermost of the tools 18 and serves for reducing the center of the bottom of the hole being drilled while, at the same time, tending to guide the tool in a straight line in the hole. Pilot. cutter 20' has a steel body 22, forged, for example, and a bar-like insert 24 of hard wear resistant material, such as cemented tungsten carbide, disposed in a central slot therein.

-is fragmentarily shownv Each tool 18', see FIG. 14, will be seen to comprise a shank 26 cylindrical in cross section and adapted for being received in one of the bores 28' of base plate 14'. Each tool 18' has a generally conical outer end 28 in which is mounted a hard wear resistant tip member 30', preferably formed of cemented tungsten carbide. The shank 26, furthermore, comprises an elongated annular groove 32' in which is mounted a split keeper element in the form of a spring clip member 34 adapted for engaging groove 36 in bore 28' for releasably retaining each tool in its respective bore.

The mouth of each bore 28 has a tapered seat 38 and each tool has a tapered shoulder 40 for engagement with the seat of the respective bore so that the tools are firmly supported in the base plate during working while, at the same time, being free to rotate therein.

Pick-type tools or cutters of the type described are known and the tools shown herein at 18' are particularly characterized in being relatively short in respect of the outer portion. For this reason, the tools 18' are extremely strong and do not break even under heavy impact.

' As will be seen in FIG. 12, each bore 28 is inclined to the vertical central plane 42' passing through the axis of base plate 14' and the center of the mouth of the respective bore so that the tools are not presented exactly endwise to the formation being cut, but somewhat at an angle when viewed from the side so that engagement of the tools with the formation will tend to cause the tools to rotate on their individual axes and, therefore, to wear down uniformly in the circumferential direction and thereby remain sharp throughout the life thereof. This angle might be, for example, about to The base plate 14 is also provided with holes 44' terminating at their lower ends about the periphery of the pilot cutter 20' and extending angularly inwardly and upwardly so as to communicate with the space above base plate 14' whereby to communicate with a central passage formed in shank 12'. Air supplied to the upper ends of holes 44' and discharged through the holes can be employed for removing chips and fines taken by the bit from the bottom of the hole being drilled to keep the bottom of the hole clean for efficient drilling operations.

In the tool shown in FIGS. 9 to 14, the body on the front side has a central plate area perpendicular to the axis of the body identified by reference numeral Surrounding the central region is an inclined annular region, identified at 17', and in which the holes for the bits or cutters are provided.

The back side ofthe cutter body is preferably concave toward the rear so that only a relatively narrow area of abutment is provided between body 14' and member 12' where welding 16 is provided.

Since the cutters or bits of the FIGS. 9 through 14 modifications must sustain relatively severe impacting, the bits are made, as shown in FIG. 14, so as to be relatively stubby outwardly from the body 14', and the carbide inserts 30' at the tips of the cutters are made larger than those described in the first mentioned modifications and engage the ends of the bodies of the cutters at a shoulder region 31. The inserts also have a shank part 33' extending into a bore in the body of the bit.

The cutters or bits shown in the first described modifications could employ the same type insert that is illustrated in FIG. 14, but generally the heavy type carbide insert of FIG. 14 is only employed where the bit or cutter is used with hard formations.

It will be appreciated that the principal difference between the tool of FIG. 1, for example, and that of FIG. 10, is in the circumferential inclination of the cutters in the tool body. In FIG. 1, where boring is accomplished by rotating the tool body while simultaneously pressing it against a formation, the bits are inclined at a substantial angle, say, about 45, in the circumferential direction and dig into the formation being worked as the tool body rotates.

In the tool of FIG. 10, the tool works principally by impacting and is rotated or indexed at a relatively low speed. The bits are thus substantially less inclined in the circumferential direction, only about 5 or 10 relative to the axis of the tool.

In both cases, however, the bits or cutters are presented point end foremost to the formation being worked and are rotatable on their respective axes, and are readilyreplaceable in the tool body when worn.

In every case, the tool is characterized by the replaceable cone shaped cutters or pick type bits which are inclined in the direction of rotation of the tool and which are free to rotate in their support blocks so as to remain sharp by distributing the wear thereon completely about the periphery. With the wear on the cutters distributed about the periphery thereof, the cutters have substantially longer life and by maintaining the points on the cutters sharp, the cutters retain an efficient cutting action throughout the life thereof.

Modifications may be made in the present invention falling within the scope of the appended claims.

What is claimed is:

I. A mining tool for boring holes in earth or mineral formations comprising; a body having a front face and adapted for rotation on an axis extending through the center of said face, said body having means at the back adapted for connection to a supporting and driving device, said body having holes extending into said front face, a plurality of pick type cutters each having a cylindrical shank detachably and rotatably retained in a respective one of said holes, each cutter having a portion symmetrical about the axis of the shank and projecting forwardly from the front face of said body and terminating in a point, said holes being distributed circumferentially and radially of said body and all being inclined to the axis of said body so as to diverge therefrom forwardly from said body.

2. A mining tool according to claim 1 in which said holes have different degrees of inclination to the axis of rotation of said body whereby the point ends of the pick type cutters are distributed radially over the region of the formation being cut.

3. A mining tool according to claim 1 which includes support blocks fixed to said body on the front side and having the said holes therein.

4. A mining tool according to claim 1 in which said body is adapted to rotate on the axis thereof and said holes are also inclined in the circumferential direction of rotation of said body.

5. A mining tool according to claim 4 in which said holes are inclined in the circumferential direction at such an angle to theaxis of said body when viewed in mining tool is advanced into a formation to be cut by simultaneously impacting the body and rotating the body. I

8. A mining tool according to claim 1 which includes a pilot cutter member on the axis of rotation of said body and fixed to said body on the front side thereof.

9. A mining tool according to claim 8 in which the front end of said pilot cutter is spaced outwardly from the front side of said body farther than the points of said pick type cutters.

10. A mining tool according to claim 9 in which the front ends of said pilot cutter and said pick type cutters are axially distributed so that the rotary tool has a substantially conical envelope with the apex toward the front of the tool.

11. A mining tool according to claim 1 which includes a support ring surrounding said body in concentric radially spaced relation thereto and substantially coplanar with the front face of said body, spoke elements fixing said ring to said body, and other pick type cutters distributed about the circumference of said ring and mounted on the side thereof facing in the same direction as the front side of said body and inclined circumferentially in the direction of rotation of said body and ring.

12. A mining tool according to claim 1 1 in which said other pick type cutters are rotatably and detachably supported by said ring and have their axes at different degrees of inclination to the axis of rotation of said body and ring.

, 13. A mining tool according to claim 12 which includes further pick type cutters mounted on said spokes and rotatable thereon and inclined circum ferentially in the direction of rotation of said body and ring.

14. A mining tool according to claim 1 in which retainers are provided retaining each pick type cutter in assembled relation with said body while not inhibiting the free rotation of the cutter in said body.

15. A mining tool according to claim 14 in which each said retainer is in the form of a resilient element having engagement with both of the pick type cutter and said body and permitting the cutter to be pried out of said body and pressed into said body.

' 16. A mining tool according to claim 1 in which said body is in the form of an auger, said pick type cutters being distributed circumferentially and radially on said auger at the leading end thereof, said pick type cutters also being distributed axially at the front end of said auger so as to lie within a conical envelope having its apex toward the front of the auger.

17. A mining tool according to claim 16 in which said pick type cutters includea group at the center of the leadin end of said an er formin a ortion ofa ilot.

18. mining tool at tcording to clzi im 17 in which said cutter.

19. A mining tool according to claim 1 in which said body is plate-like and is adapted at the back for being welded to a support member.

20. A mining tool according to claim 19 in which said body on the front side has a central area perpendicular to the axis of said body and an annular area surrounding said central area and inclined :rearwardly,said holes being formed in said annular area. I

21. A mining tool according to claim 20 in which the back side of said body is concave toward the rear of the body.

22. A mining tool according to claim 1 which includes fluid passage means extending axially through port in the front face of said body.

. il l' l 

1. A mining tool for boring holes in earth or mineral formations comprising; a body having a front face and adapted for rotation on an axis extending through the center of said face, said body having means at the back adapted for connection to a supporting and driving device, said body having holes extending into said front face, a plurality of pick type cutters each having a cylindrical shank detachably and rotatably retained in a respective one of said holes, each cutter having a portion symmetrical about the axis of the shank and projecting forwardly from the front face of said body and terminating in a point, said holes being distributed circumferentially and radially of said body and all being inclined to the axis of said body so as to diverge therefrom forwardly from said body.
 1. A mining tool for boring holes in earth or mineral formations comprising; a body having a front face and adapted for rotation on an axis extending through the center of said face, said body having means at the back adapted for connection to a supporting and driving device, said body having holes extending into said front face, a plurality of pick type cutters each having a cylindrical shank detachably and rotatably retained in a respective one of said holes, each cutter having a portion symmetrical about the axis of the shank and projecting forwardly from the front face of said body and terminating in a point, said holes being distributed circumferentially and radially of said body and all being inclined to the axis of said body so as to diverge therefrom forwardly from said body.
 2. A mining tool according to claim 1 in which said holes have different degrees of inclination to the axis of rotation of said body whereby the point ends of the pick type cutters are distributed radially over the region of the formation being cut.
 3. A mining tool according to claim 1 which includes support blocks fixed to said body on the front side and having the said holes therein.
 4. A mining tool according to claim 1 in which said body is adapted to rotate on the axis thereof and said holes are also inclined in the circumferential direction of rotation of said body.
 5. A mining tool according to claim 4 in which said holes are inclined in the circumferential direction at such an angle to the axis of said body when viewed in the radial direction of said body that rotation of said body while simultaneously pressing it iN the forward direction will present said cutters point end foremost to the formation to be cut.
 6. A mining tool according to claim 4 in which said holes are inclined in the circumferential direction at an angle of from about 5* to 10* when viewed in the radial direction of said body.
 7. A mining tool according to claim 6 in which said mining tool is advanced into a formation to be cut by simultaneously impacting the body and rotating the body.
 8. A mining tool according to claim 1 which includes a pilot cutter member on the axis of rotation of said body and fixed to said body on the front side thereof.
 9. A mining tool according to claim 8 in which the front end of said pilot cutter is spaced outwardly from the front side of said body farther than the points of said pick type cutters.
 10. A mining tool according to claim 9 in which the front ends of said pilot cutter and said pick type cutters are axially distributed so that the rotary tool has a substantially conical envelope with the apex toward the front of the tool.
 11. A mining tool according to claim 1 which includes a support ring surrounding said body in concentric radially spaced relation thereto and substantially coplanar with the front face of said body, spoke elements fixing said ring to said body, and other pick type cutters distributed about the circumference of said ring and mounted on the side thereof facing in the same direction as the front side of said body and inclined circumferentially in the direction of rotation of said body and ring.
 12. A mining tool according to claim 11 in which said other pick type cutters are rotatably and detachably supported by said ring and have their axes at different degrees of inclination to the axis of rotation of said body and ring.
 13. A mining tool according to claim 12 which includes further pick type cutters mounted on said spokes and rotatable thereon and inclined circumferentially in the direction of rotation of said body and ring.
 14. A mining tool according to claim 1 in which retainers are provided retaining each pick type cutter in assembled relation with said body while not inhibiting the free rotation of the cutter in said body.
 15. A mining tool according to claim 14 in which each said retainer is in the form of a resilient element having engagement with both of the pick type cutter and said body and permitting the cutter to be pried out of said body and pressed into said body.
 16. A mining tool according to claim 1 in which said body is in the form of an auger, said pick type cutters being distributed circumferentially and radially on said auger at the leading end thereof, said pick type cutters also being distributed axially at the front end of said auger so as to lie within a conical envelope having its apex toward the front of the auger.
 17. A mining tool according to claim 16 in which said pick type cutters include a group at the center of the leading end of said auger forming a portion of a pilot.
 18. A mining tool according to claim 17 in which said pilot includes a center cutter fixed to said auger on the axis thereof to rotate therewith and said group of pick type cutters are individually rotatable on said body and are circumferentially distributed about said central cutter.
 19. A mining tool according to claim 1 in which said body is plate-like and is adapted at the back for being welded to a support member.
 20. A mining tool according to claim 19 in which said body on the front side has a central area perpendicular to the axis of said body and an annular area surrounding said central area and inclined rearwardly, said holes being formed in said annular area.
 21. A mining tool according to claim 20 in which the back side of said body is concave toward the rear of the body. 